1. Field of the Invention
The invention relates to polycarbonate resins and more particularly relates to branched or cross-linked, fire-resistant polycarbonate resins and intermediates thereto.
2. Brief Description of the Prior Art
Polycarbonate resins have found wide usage to fabricate a wide variety of articles such as automotive component parts. Polycarbonate resins of the present invention include ones that are cross-linked to enhance their properties of fire resistance and particularly the characteristic of "non-dripping" when exposed to high temperatures and open flames. The term "non-dripping" as used herein means that when exposed to high temperatures, particularly open flame, articles molded from the resins do not "melt" or liquify so as to form liquid drops (drippings).
A wide variety of copolyester-carbonate resins are also known in the prior art as is the method of their preparation; see for example U.S. Pat. No. 4,487,896.
Copolycarbonates of bisphenol-A and 4,4-bis(4-hydroxyphenyl) alkanoates were described by Fischer, et al., Journal of Applied Polymer Science, Vol. 10, pp. 245-252 (1966).
The U.S. Pat. No. 3,285,875 to Battenbruch et al. describes the cross-linking or "curing" of polycarbonate resins by a transesterification method, resulting in a molecular weight build-up of the resin. The method mandates the use of a transesterification catalyst.